The present disclosure relates to a micromechanical method and a corresponding assembly for bonding semiconductor substrates and a corresponding bonded semiconductor chip.
Although applicable to any micromechanical components and structures, in particular sensors and actuators, the present disclosure and the problem area addressed thereby will be explained with regard to a micromechanical sensor that can be produced using the technology of silicon surface micromachining.
Micromechanical substrate connections, e.g. wafer-wafer bonding connections, are usually realized by eutectic alloys comprising two or more solid bonding materials or alloy components as constituents. Eutectic alloys of this type have an unambiguously determinable melting point. By contrast, other mixing ratios with the same alloy components have a melting or solidification range in which, alongside the melt, a solid phase is also present. The melting point of the eutectic alloy is, moreover, the lowest of all mixtures composed of the same constituents.
During the bonding process, a minimum required bonding force has to be applied in order to bring the bonding alloys into contact at the wafer level. This causes the liquid eutectic phase to flow. In this case, it can happen that the liquid eutectic phase flows into MEMS functional regions in an uncontrolled manner. In order to minimize or prevent such flowing, it is possible to provide, for example, a very wide stop trench in each case on the inside and outside around the bonding frame, as a result of which an increased area requirement at the chip level has to be kept available.
FIG. 5 is a schematic partial plan view of a chip region of an exemplary assembly for bonding semiconductor substrates.
The micromechanical sensor chip 1, which has an active functional region 4 and a passive edge region 4a. Provided in the edge region 4a is a bonding frame 2 with an applied eutectic bonding alloy, for example Al—Ge, which divides the edge region 4a into an inner region 4a2, which is surrounded by the bonding frame, and an outer region 4a1. A stop trench 3 lies in the inner region 4a2 between bonding frame 2 and functional region 4 of the sensor chip 1, said stop trench being intended to prevent melt from flowing from the region of the bonding frame 2 into the functional region 4 during the bonding process. The part of the melt flowing during the bonding process is therefore intercepted by the use of the stop trench 3. Typical dimensions of such a stop trench 3 are between 20 and 50 μm in terms of the width b. Said stop trench 3 additionally requires both a minimum distance d1 with respect to the bonding frame 2 and a minimum distance d2 with respect to the active functional region 4. As a result, an inconsiderable area requirement is necessary precisely in the case of sensor chips that are becoming ever smaller.
WO 2005/008772 A2 discloses an electronic component comprising a semiconductor chip and a lead frame having a metal coating pattern on its underside for the soldering of the electronic component. Said metal coating pattern has wetting regions, which can be wetted with solder material, and anti-wetting regions, which cannot be wetted with solder material, wherein the electronic component has solder deposits on the wetting regions on the underside.